Avian influenza virus is a generic name for influenza A viruses that mainly infect birds, and wild water birds are their natural hosts. Some avian influenza viruses infect domestic poultry, such as chickens, quails, and turkeys, leading to highly pathogenic infection. The chicken industry is facing a worldwide threat from such highly pathogenic avian influenza viruses.
Although development and research of vaccines for preventing avian influenza virus infection have been conducted (see for example, Patent Document 1), no vaccine is currently available that can completely prevent avian influenza virus infection. The actual measure taken when an avian influenza virus infection actually breaks out is therefore to immediately destroy domestic poultry within a several-kilometer radius from the breakout site. The infection of H5N1 subtype virus, a subtype of avian influenza virus, has also been reported to occur in humans upon contact with a large amount of the virus or due to constitutional predisposition of a host.